Bacteroides are now recognized as major pathogens in various infections and especially in those consequent to bowel surgery which is frequently if not primarily due to cancer of the colon. These organisms cause extensive destruction and considerable mortality in such cases. Yet, little is known of their mechanisms of pathogenesis or what converts them from commensals to destructive invaders. We plan to use three groups of such bacteria: type strains from the ATCC, clinical isolates from our own hospital, and clinical isolates from other hospitals about the U.S. and from abroad. These will be studied using new and improved culture methods involving chemically defined media already perfected in our laboratory in order to better understand the following aspects: (1) the occurrence, abundance and chemical nature of cellular lipopolysaccharides - at present a most unclear and contentious subject; (2) the ability of these microorganisms to digest and perhaps utilize significant host tissue constituents including glycoproteins, sphingo- and glycolipids, mucopolysaccharides, collagen, and elastin. These studies are intended to help resolve the question of what specific types of damage such pathogens produce and how better to perceive, prevent or at least minimize such effects in infections produced by them. Of prime concern here is the striking frequency of surgical procedures intended to alleviate malignancies of the bowel being negated in a few days post-operative by overwhelming Bacteroides infections.